1. Field of the Invention
This invention relates to a dual span center pivot irrigation system and more particularly to the controls for independently operating and coordinating the movement of each of spans of the center pivot irrigation system relative to one another in at least three different modes. Each of the center pivot span structures is pivotally secured to a fixed center pivot structure and is supported upon one or more self-propelled drive units for pivotally moving the span structure relative to the center pivot structure.
2. Description of the Related Art
Optimal plant husbandry requires adherence to the art of irrigation with a fair degree of precision. While established plants can tolerate over watering and under watering to a certain degree, seeds and seedlings are not so tolerant. Efficient farming practices demand a very specific seed density with a relatively high germination rate. Improper irrigation results in gaps or irregularities in seed density, and improper watering of the seeds will have a deleterious effect in achieving a proper germination rate.
Extremely small seeds, such as carrot seeds, have a very poor germination rate using conventional irrigation techniques. The primary problem associated with the conventional irrigation techniques with respect to small seeds involves controlling the amount of irrigation liquid (e.g., water) and its effect on the seed exposed on a surface for germination. Because the very small seeds are unduly influenced by heavy water application, small seeds will fail to stay in a designated spot and will wash away with the irrigation water, thereby increasing the seed density in one area to the exclusion of other areas
There are two basic types of conventional irrigation, Center Pivot and Solid Set. In a conventional center pivot irrigation system, a fixed center pivot structure is provided which includes a vertically disposed water supply pipe supported thereon which is in communication with a source of irrigation water under pressure. The center pivot span structure is pivotally secured at its inner end to the center pivot structure and includes a water delivery pipe supported on one or more self-propelled drive units with the inner end of the water delivery pipe being in fluid communication with the vertically disposed water supply pipe. In operation, the center pivot span structure pivots or rotates in a circle, or portions thereof, about the fixed center pivot structure. Inasmuch as the center pivot span structure rotates in a 360-degree circle, in normal situations, one revolution of the center pivot span structure results in a complete irrigation of the underlying area contained beneath the span structure. One complete revolution of the center pivot span structure normally consumes a considerable amount of time such that successive passes over the same area will not occur frequently enough for small seeds and the seedlings growing therefrom. Thus, the farmer is faced with the difficult choice of applying a relatively fine mist of water to the delicate seeds on an intermittent basis and hoping that a high germination rate results therefrom. Inasmuch as soil can only absorb the irrigation liquid at a certain rate, the farmer is limited with respect to the amount of water that may be dispensed on a single pass versus the amount of time that successive passes can occur with a single center pivot span structure. Thus, the dilemma heretofore faced by the farmer is the delicate balancing of a spray rate per single pass of a single center pivot span structure versus the absorption capability of the underlying soil and the seed size to retain the seed in the desired location while preventing the washing of soil or other matter which will cover up the seeds.
In a conventional Solid Set irrigation system, an irrigation pipe network placed above ground throughout the filed is provided which includes evenly space vertical pipes, typically terminated with impact sprinklers place at a height slightly above a mature crop canopy. The irrigation pipe network is in communication with a source of irrigation water under pressure. In operation, a valve is opened allowing water to be distributed though the pipe network and impact sprinklers. Due to the design of impact sprinklers, prior to full water pressure in the pipe, the water distributed through the impact sprinklers floods or “dribbles” onto the field. In a similar manner, as the water pressure is turned off, instead of instantly shutting off the water distribution through the impact sprinklers, the water floods or “dribbles” onto the field as water pressure is lost. The effects of turning water ON and OFF through the impact sprinklers of Solid Set irrigation results in a redistribution of small seedlings know as wash-out. Because the irrigation pipe network is located above ground, this wash-out effect can also be the result of a break in the pipe network. Also associated with a conventional Solid Set irrigation system is the associated labor. Because the irrigation pipe network is located above ground, the network must be assembled and disassembled at various times throughout the growing season to accommodate various cultivation and harvesting equipment.
In the pending provisional application Ser. No. 60/651,011 filed Feb. 8, 2005, and entitled IRRIGATION SYSTEM HAVING TWO OR MORE SPANS EXTENDING FROM A CENTER PIVOT STRUCTURE, several patents were discussed in the Background of the Invention portion of the application. None of/the prior art patents disclosed in the pending application involves the use of two or more center pivot span structures which pivotally extend outwardly from a center pivot structure and which are independently driven. In the provisional application, a disclosure is made of two or more center pivot span structures pivotally secured to a fixed center pivot structure and which extend outwardly therefrom with the span structures being independently driven to achieve the desired irrigation of small seeds or the like. Although the concept of two or more center pivot span structures extending outwardly from a center pivot structure is disclosed in the provisional application, the control means and the operational safeties involved therewith were not disclosed in detail. The subject of this invention is the control means and the safeties associated therewith for operating at least a pair of center pivot span structures which radially extend outwardly from a center pivot structure with the center pivot span structures being operated in various modes such as: (1) independent wiper; (2) follow the leader; and (3) independent full circle.